1. Field of the Invention
This invention is directed to methods for separating drilling fluid from a mixture of such fluid and lost circulation materials and to apparatuses useful in such methods.
2. Description of Related Art
Often in drilling a wellbore, the circulation of drilling fluid to and then away from the drill bit ceases due to the porosity of the formation and/or due to fracturing of the formation through which the wellbore is being drilled. Drilling fluid pumps into the fractured formation rather than being returned to the surface. When circulation is lost, it is usually supposed that the lost circulation occurred at some specific depth where the formation is xe2x80x9cweakxe2x80x9d, and that the fracture extends horizontally away from the borehole. Expressions used to describe rocks that are susceptible to lost returns include terms like vugular limestone, unconsolidated sand, xe2x80x9crottenxe2x80x9d shale, and the like. Whether fractures induced by excessive mud pressure are parallel to the axis of the borehole (vertical) or perpendicular to the axis of the borehole (horizontal) is a subject of some controversy.
To fill or seal off a porous formation or to fill or seal off a wellbore fracture so that a proper route for drilling fluid circulation is re-established, a wide variety of xe2x80x9clost circulation materialsxe2x80x9d have been pumped into wellbores. For purposes of classification, some lost circulation materials can generally be divided into fibers, flakes, granules, and mixtures.
In certain prior art screens, square mesh wire cloths have been used with relatively fine wire diameters in multiple layers because of their resistance to blinding, e.g. with one or more support layers and two screening layers. The ratio between these meshes has generally been between about 1.1 and 1.7. Certain of these screen combinations have difficulty in handling LCM material and the material often blinds these screens. Oblong opening meshes with length to width ratios between 1.55 and 2.0 have also been used in the past for their resistance to blinding. As the ratio increases between the meshes, blinding decreases but strength also decreases. As the wire diameter increases, the resistance to blinding decreases, but the strength increases. However, when multiple layers of oblong cloths have been used in certain prior art screens, the ratio of the length of the openings at adjacent layers has been 2 or greater and of the width of the openings of adjacent layers has been 1.6 or greater. Attempts have been made to use oblong meshes with increasingly large ratios.
Typical known shale shaker screens or screen assemblies with square mesh openings often are clogged when attempts are made to separate lost circulation materials from a mixture of them with fluid that has been pumped down a wellbore. Stringy, fibrous, and/or fibril material (xe2x80x9cfibrousxe2x80x9d material) can wrap around a wire of a screen and/or bridge a mesh opening without passing through the screen. In certain particular circumstances there have been problems with commercially available ULTRA-SEAL lost circulation material that has fibrous material in it. If components of this material which swell are caught between two screen mesh layers, they swell and plug the screen rather than going through the screen with the drilling fluid (while drilled cuttings, debris, etc. move on the top of the screen assembly and exit the shaker or vibratory separator apparatus). Although the prior art discloses the use of screens with non-square openings for use on shale shakers for treating mixtures of drilling fluid and drilling solids, the present inventors are unaware of the use of prior art screen(s) and/or screen assemblies with non-square mesh openings in methods for separating fluid and fibrous lost circulation materials from drilled cuttings and believe it is not obvious to use screens with non-square openings with relatively more opening area to successfully treat such fluids.
FIGS. 1A and 1B show a prior art screen 22 as disclosed in U.S. Pat. No. 2,723,032 with a coarse mesh wire screen, or cloth 23 that provides a backing screen or cloth of the unit. A fine mesh wire screen 24 is superimposed or mounted upon the backing screen 23. The screen unit 22 has its coarse backing wire mesh or cloth coated or covered preferably with rubber or some suitable rubber or synthetic rubber composition. The strands are indicated at 25 and the covering or coating at 26. Since all of the strands 23 are coated or covered, there is, of course, rubber-to-rubber contact between these strands of the coarser mesh screen 23. The backing screen of cloth 23 is of the roller flat-top type and of any coarse size such, for example, as three or four mesh. The mesh of the finer mesh wire screen 24 varies, in accordance with the separating job to be done. For example, the mesh of the fine wire screen or cloth 24 may vary from the order of minus 20 (xe2x88x9220) to the order of minus 325 (xe2x88x92325).
FIGS. 2A and 2B disclose a screen 30 as disclosed in U.S. Pat. No. 4,696,751 with a first mesh screen with rectangular dimensions of width and length. A second screen 38 is held in superimposed abutting relationship to the first screen 32. The second 38 has width and length dimensions. The length dimensions of the first screen is larger than length dimension of the second screen, and the width dimension of the first screen is smaller than the width dimension of the second screen.
FIGS. 3A and 3B disclose screens 50 and 53 shown in U.S. Pat. No. 5,626,234 which has an upper cloth 51 and lower cloth 52. The upper cloth 51 is formed from woven stainless steel wire in the range 0.19 mm to 0.036 mm diameter and 60-325 mesh, (i.e. number of strands per inch) while the lower cloth 52 is formed from woven phosphor bronze wire in the range 0.45 mm to 0.19 mm diameter and 20-40 mesh. A screen 53 in FIG. 3B has an upper cloth 54 like the upper cloth 51 (FIG. 3A) and a lower cloth 55 woven from stainless steel wire having a nominal diameter in the range 0.20 to 0.45 mm diameter and typical 30 mesh, and is coated with an epoxy based material, or Molybdenum Disulphide, or Teflon (Registered Trade Mark), to a thickness in the range 5 to 50 microns typically 20 to 40 microns. Multiple passes of the wire through a coating process or through a succession of such processes may be necessary to achieve the desired coating thickness. The wires 57, 58, 59 are shown in cross-section to show the outer material coatings 67, 68, 69 (not to scale). The wire 64 is shown with the coating scraped from one end.
There has long been a need for a method for efficiently and effectively separating fluid and fibrous lost circulation materials from a mixture of them with drilled cuttings, debris, etc. There has long been a need, recognized by the present inventors, for such a method that does not result in clogged or plugged screen assemblies used for such separating.
The present invention, in certain aspects, discloses methods for separating fluid and fibrous lost circulation material from a mixture of fluid, drilled cuttings and fibrous lost circulation material, the methods including: introducing the mixture onto a screen assembly that is vibrating, e.g., vibrated in a shale shaker, for passage of the fluid and fibrous lost circulation material through the screen assembly and for separation from the mixture of drilled cuttings, the screen assembly having at least two layers of screening material one on top of the other and including at least a first layer over a second layer, each layer having screen mesh with rectangular openings as viewed from above, the first layer having first rectangular openings, and the second layer having second rectangular openings, each of the first rectangular openings having a first width and a first length, and each of the second rectangular openings having a second width and a second length, the ratio of the first length to the first width ranging between 1.55 and 2.00, the ratio of the second length to the second width ranging between 1.55 and 2.00, the ratio of the first length to the second width ranging between 0.95 and 1.05, and the lengths of the first rectangular openings are parallel to lengths of the second rectangular openings; and in one particular aspect the ratio of the first length to the first width is about 1.6, the ratio of the second length to the second width is about 1.7, and the ratio of the first length to the second width is about 1.0. Such a screen assembly may have a screen support, e.g, but not limited to, any strip support, frame, or plate discussed or referred to below.
The present invention, in certain aspects, discloses a method for using a vibratory separator with one or more screen assemblies to separate fluid from a mixture of such fluid and fibrous lost circulation material that is pumped down a wellbore in an effort to remedy a lost circulation problem so that the fluid to be recovered and the fibrous lost circulation material passes through the one or more screen assemblies and the drilled cuttings, etc. move off the top of the one or more screen assemblies. In one aspect such a method employs a screen or screen assembly that has at least one layer of screen mesh that has non-square openings, e.g. but not limited to non-square rectangular openings. Fluid flow across such a screen or screen assembly may be in the lengthwise direction of the no-square openings or transverse to the length. It is within the scope of the present invention to use any suitable known vibratory separation apparatus or shale shaker with one or more screen assemblies according to the present invention in methods according to the present invention.
In certain particular aspects such a method employs a screen assembly with a lowermost screen of relatively large mesh, e.g. between 15 and 50 mesh; a middle screen of between 105xc3x9764 and 170xc3x97105 mesh (i.e. 105 openings in one direction, 64 openings in the other, 170 openings in one direction 105 openings in the other direction) or a middle screen of between 46xc3x9729 and 145xc3x9790 mesh;) with openings that are non-square rectangular openings between 333.4 and 178.4 microns long and between 198.7 and 106 microns wide, or between 425 and 127 microns long and between 748 and 234 microns wide; and a top mesh between 240xc3x97150 and 170xc3x97105 (or 76xc3x9749) mesh with non-square rectangular openings that are about 136.3 to 72.8 microns wide and 198.7 to 106 microns long. Wire between about 0.016 to 0.0045 inches in diameter is used for the lowermost screen; between 0.0014 to 0.0025 inches in diameter for the middle screen; and between 0.0012 and 0.0018 inches in diameter for the top screen. Alternatively any screen pattern or weave with any wires disclosed herein may be used.
In certain aspects by using non-square rectangular openings a larger opening area is presented to a fiber than is presented by a square opening with a side equal to the width of the rectangular opening (i.e. the length of the non-square rectangular opening is longer than the length of the side of the square). A fiber caught on a wire and/or bridging such a non-square rectangular opening while connected to one or two wires or laying across two wires of such an opening, does not block flow through the non-square opening to the extent that such a fiber would block flow through the square opening, i.e. the percentage of area of the non-square opening blocked by the fiber is less than the percentage of the total area of the square opening that would be blocked by the fiber. In certain aspects in such a situation there may also be more fluid flow against such a fiber and past the fiber""s surfaces when using the non-square openings as compared to the amount of such fluid flow through a square opening. Thus loosening and/or wash through of the fiber may be facilitated by using the non-square openings. Such facilitation may be further enhanced by flowing the fluid to be treated in the general direction of the length of the non-square rectangular openings.
In certain prior art screens that use square mesh openings fibrous lost circulation material can become trapped between the top two meshes of a screen. This is inhibited or reduced by using screens according to the present invention with non-square openings as described above.
It is contrary to the accepted teaching and skill in the art to use screens with the relatively large non-square openings to separate fluid from fibrous lost circulation materials. For those solids that are in a mixture to be treated and are to be moved off the top of the screen assemblies and that are generally spherical and therefore have a largest dimension; the width (not the length) of a rectangular opening determines if the solids will or will not pass through such an opening and the relatively longer length of the rectangular opening permits fibrous material to pass through with the fluid to be recovered that passes through the screen assemblies. To achieve this in certain aspects the middle or second from the top of a multi-layer screen assembly has oblong or rectangular openings (as viewed from above) to assist the passage of fibrous lost circulation material through the screen assembly and to speed the passage of such materials through the screen assembly so that they are not resident between screen layers a sufficient amount of time to cause plugging problems by swelling. In other aspects the top layer of screening material may also have such oblong or rectangular openings. Also, the length of the openings in the middle or second-from-the-top layer may be parallel to the lengths of the openings of the top layer or these lengths may be at right angles or at any desired angle to each other (as viewed from above).
What follows are some of, but not all, the objects of this invention. In addition to the specific objects stated below for at least certain preferred embodiments of the invention, other objects and purposes will be readily apparent to one of skill in this art who has the benefit of this invention""s teachings and disclosures. It is, therefore, an object of at least certain preferred embodiments of the present invention to provide:
New, useful, unique, efficient, nonobvious methods for separating fluid and fibrous lost circulating material from a mixture that includes drilled cuttings;
Such methods in which the clogging or plugging of screens of a vibratory separator is inhibited;
Such methods in which screens with non-square openings, e.g. generally oblong or rectangular openings, are used;
Such methods in which the resident time in a screen assembly of material that can swell is reduced and the passage of such material through the screen assembly is facilitated;
Such methods in which fluid flow is in the general direction of the length of the non-square openings (of either a top layer of screening material of a screen assembly or a layer below the top layer) or transverse thereto; and
Such methods in which a multi-screen screen assembly is used.
Such methods in which a multi-screen screen assembly is used.
The present invention, in certain aspects, discloses a screen with wires of varying diameter in a single screen cloth layer. In one aspect, alternate wires (e.g. but not limited to, every other wire, every third wire, every fourth wire, or every fifth wire) in a screen warp direction are of a larger diameter than the other wires of the screen. In other aspects, alternate wires (e.g. but not limited to, every other wire, every third wire, every fourth wire, or every fifth wire) in a screen shute direction are of a larger diameter than the other wires of the screen. Alternatively, all wires in a warp direction or in a shute direction may be of the larger diameter.
It is, therefore, an object of at least certain preferred embodiments of the present invention to provide:
New, useful, unique, efficient, nonobvious methods for screening lost circulation material with vibratory separators; and
New useful, unique, efficient, nonobvious vibratory separators (e.g. shale shakers) with such screens.
Certain embodiments of this invention are not limited to any particular individual feature disclosed here, but include combinations of them distinguished from the prior art in their structures and functions. Features of the invention have been broadly described so that the detailed descriptions that follow may be better understood, and in order that the contributions of this invention to the arts may be better appreciated. There are, of course, additional aspects of the invention described below and which may be included in the subject matter of the claims to this invention. Those skilled in the art who have the benefit of this invention, its teachings, and suggestions will appreciate that the conceptions of this disclosure may be used as a creative basis for designing other structures, methods and systems for carrying out and practicing the present invention. The claims of this invention are to be read to include any legally equivalent devices or methods which do not depart from the spirit and scope of the present invention.
The present invention recognizes and addresses the previously-mentioned problems and long-felt needs and provides a solution to those problems and a satisfactory meeting of those needs in its various possible embodiments and equivalents thereof. To one skilled in this art who has the benefits of this invention""s realizations, teachings, disclosures, and suggestions, other purposes and advantages will be appreciated from the following description of preferred embodiments, given for the purpose of disclosure, when taken in conjunction with the accompanying drawings. The detail in these descriptions is not intended to thwart this patent""s object to claim this invention no matter how others may later disguise it by variations in form or additions of further improvements.